Implantable medical devices are well known in the field of endoluminal treatment of medical conditions and comprise a wide variety of types. In general, medical devices are either self-expandable or expandable by a delivery mechanism of an introducer assembly. Self-expandable devices may be made of a material having inherent expansion properties, such as spring steel or other resilient material, including metals, metal alloys and also polymers and the like. Self-expandable devices may also be made of shape memory material, such nickel titanium alloy (for instance Nitinol). Such devices will expand into a vessel as soon they are released from the delivery constraining mechanisms.
A problem with self-expandable devices is that in order to ensure their proper operation they are generally sized to apply constant pressure on the vessel walls, which over time can impair the integrity of the vessel.
Devices which are not self-expandable, that is which are expanded by a separate device, can be fitted to a vessel more precisely and more reliably, while generally avoiding some of the issues encountered with self-expanding devices. A common deployment method for such devices involves the use of an inflatable delivery balloon. The device is loaded and crimped onto the deflated and often wrapped balloon, passed endovascularly to the treatment point and then the balloon inflated to expand the device until it presses against the vessel wall. Once expanded, the balloon is deflated and removed from the patient, leaving the device implanted in the vessel. In many instances it is preferable to use such a balloon expandable medical device.
However, there are some known issues with deployment by inflatable balloons, typically sliding of the medical device during the deployment procedure, which can lead to incorrect placement of the device in the vessel, to incomplete expansion of the device and at worst to an abortive procedure. Attempts have been made to try to secure such devices to the balloon, for instance by shaping the balloon to have one or more inflatable ribs which can engage with a part of the device to hold it in position. However, ribs and other shaping features of this nature tend to flatten on inflation of the balloon, leading to loss of the holding feature. Other attempts have involved adding to the balloon one or more ridges or other protruding elements of solid form to engage the medical device. Such elements provide better retention of the medical device on the delivery balloon but usually at the expense of adding bulk to the balloon, which impairs its compressibility, as well as in some cases reducing its flexibility when deflated. A less flexible and a less compressed balloon can adversely affect the trackability of the balloon through a patient's vasculature and also the size of vessel which can be treated.
Examples of prior art balloon-based delivery devices can be found in U.S. Pat. No. 5,935,135, EP-0,714,640, US-2011/0152997, US-2002/0120321, EP-1,132,059, U.S. Pat. No. 6,942,681, US-2003/0032999, U.S. Pat. Nos. 5,836,965, 5,976,181, 6,022,359, 6,027,510, 6,110,192, 6,764,504, US-2005/0049608 and US-2004/0138731, among others.